This invention relates to a method of operation for a vehicle electronic throttle control (ETC) system, and more particularly to a method of using the throttle control system to govern vehicle acceleration, speed and power during a fault.
In a vehicle ETC system, the engine throttle plate is mechanically de-coupled from the driver-operated accelerator pedal, and instead is positioned by an electric motor under the control of an electronic or powertrain control module (PCM). The motor is activated to position the throttle plate in response to accelerator pedal movement, but may also be controlled to achieve other functions such as idle speed control, engine speed governing, cruise control, torque reduction for traction control, and vehicle acceleration governing. In general, the PCM or another controller determines a desired effective throttle area to achieve a given function, and the PCM activates the motor to move the throttle plate to a position corresponding to the desired throttle area. In addition to electronic throttle control, the PCM can regulate vehicle acceleration and engine power with the fuel injectors or spark retard.
The present invention concerns an improved method of vehicle acceleration governing an ETC system. The acceleration governing function is typically requested under certain fault conditions, such as a sensor fault, and operates under such fault conditions to limit the vehicle acceleration to a threshold value, which may be determined based on a change in vehicle speed. Sensor faults may include, but are not limited to, an airflow sensor fault, and pedal or throttle sensors generating an out-of-range value. The throttle limits the vehicle acceleration and engine power by limiting the throttle area to a predetermined calibrated value during such a fault condition. On flat driving conditions at sea level, this limited calibrated throttle area will correspond to a vehicle speed, but during operation on terrain inclinations, at altitude, or during high power or torque demand operating conditions such as towing, this limited throttle area may not be great enough to ensure a minimum speed. Thus, the limited speed produced by the fixed throttle limit is heavily dependent on operating environment and vehicle loading. This invention overcomes these limitations while maintaining a safe vehicle response during a sensor failure. When sufficient redundancy exists (such as having two brake indications and two vehicle speed readings), it would be desirable to allow full throttle operation if acceleration can be limited. The present invention will monitor vehicle speed and acceleration and allow the throttle plate to move to a position beyond its limited calibrated throttle area during a fault condition to allow a desired torque output during a high power torque demand operating condition.